We propose that acute lung injury paradigms are likely to be characterized by unique endothelial injury "fingerprints" based on the Ca2+ entry pathways they target and the expression pattern of these channel proteins. Members of the canonical subfamily of transient receptor potential (TRP) proteins comprise subunits of store-operated Ca2+ channels and participate in Ca2+ entry-dependent regulation of lung endothelial permeability in extra-alveolar vessels. Our observation that heart failure leads to loss of the permeability response to store depletion but not that to 14,15-epoxyeicosatrienoic acid (14,15-EET), a lipid that promotes Ca2+ entry-dependent acute lung injury only in alveolar septal capillaries, suggests that 14,15- EET targets a distinct channel expressed in the septal microvasculature. Our preliminary data suggests a novel candidate - TRPV4 - a member of the vanilloid subfamily of TRP proteins. We HYPOTHESIZE that regulation of TRPV4 channels expressed in alveolar septal endothelium integrates the Ca2+ entry-dependent permeability response to diverse stimuli, including heat, EETs, and high vascular pressure. Further, we hypothesize that TRPV4-dependent permeability responses in septal capillary endothelium are independent of store-operated Ca2+ entry pathways, and thus should be retained in chronic heart failure. AIM 1 will determine whether TRPV4 is a common target by which EETs and mechanical perturbation promote Ca2+ influx required for increased endothelial permeability in the alveolar septal compartment of the lung, and whether temperature sets the gain of this response. AIM 2 will reveal whether TRPV4-mediated endothelial permeability responses in septal capillaries are retained in chronic heart failure, a model in which storeoperated TRPC channels are down-regulated. We will address these aims using specific measures of permeability and Ca2+ entry in isolated rat and mouse lung, microscopy of lung and vascular corrosion casts to map spatial heterogeneity in the permeability response, pharmacological tools to manipulate signaling pathways implicated in gating of TRPV4, and TRPV4-/- mice. This work will provide the first rigorous analysis of TRPV4 channel expression linked to regulation of endothelial permeability in the intact lung microvasculature.